The invention relates to a method and an apparatus for coating a substrate, especially with electrically nonconductive coatings from electrically conductive targets in a reactive (e.g., oxidizing) atmosphere, comprising a power source which is connected to cathodes containing magnets and disposed in an evacuable coating chamber, which cathodes cooperate electrically with the targets, which deposit themselves on the substrate. Anodes are disposed separated electrically from one another and from the sputtering chamber and are provided in a plane between the cathodes and the substrate.
A sputtering apparatus for the production of thin coatings is known (DD 252,205), comprising a magnet system and, disposed above it, at least two electrodes of the material to be sputtered, these electrodes being electrically configured such that they are alternately the cathode and anode of a gas discharge. For this purpose the electrodes are connected to a sinusoidal alternating voltage of preferably 50 Hz.
This known sputtering apparatus is to be especially suitable for the deposit of dielectric coatings by reactive sputtering. By operating the apparatus at about 50 Hz it is desired to prevent the occurrence of glitter on the anode and, in the case of metal coating, to prevent electrical shorting (so-called "arcing").
In another already known apparatus for sputtering a thin film, in which the rate of speed with which coatings of different materials can be deposited is controllable (DE 39 12 572, to which U.S. Pat. No. 4,956,070 corresponds) in order thus to arrive at extremely thin layer packs, at least two different kinds of counterelectrodes are disposed on the cathode side.
Also known is a system for depositing a metal alloy by means of radiofrequency cathode sputtering (DE 35 41 621) in which two targets are alternately activated, and the targets contain the metal components of the metal alloy to be deposited, but in different proportions. The substrates are for this purpose disposed on a substrate holder which is set in rotation by a drive unit during the sputtering process.
It is furthermore known, through a prior published printed disclosure (DE 38 02 852), in the case of an apparatus for coating a substrate with two electrodes and at least one material for sputtering, to dispose the substrate between the two electrodes at a distance apart and select the half-waves of the alternating current to serve as low-frequency half-waves of substantially equal amplitudes.
According to another prior published printed disclosure (DE 22 43 708), a method for the production of a glow discharge is known, which has an electrode arrangement placed in a working gas, to which a working voltage is applied, the method being characterized by the production of a magnetic field which together with the electrode arrangement results in at least one trap for holding virtually all electrons emitted by the electrode arrangement which have sufficient energy to ionize the working gas. For this process an electrode arrangement is used in which the electrodes are provided in pairs. In particular, this disclosure also describes hollow electrodes in whose interior a glow discharge can be produced, the electrodes being in the form of tube shells.
A method and an apparatus is furthermore described in an older, not previously published patent application (German P 41 06 770.3 to which U.S. Pat. No. 5,169,509 corresponds) for the reactive coating of a substrate with an electrically insulating material, for example with silicon dioxide (SiO.sub.2), comprising an alternating current source which is connected to cathodes enclosing magnets disposed in a coating chamber, which cooperate with targets, two ungrounded output terminals of the alternating current source being connected each to a cathode bearing a target, the two cathodes being placed side by side in a plasma space in the coating chamber and being each at about the same distance away from the oppositely lying substrate. The effective level of the discharge voltage is measured by an effective-voltage detector connected by a conductor to the cathode and delivered as D.C. voltage by a conductor to a controller which by means of a regulating valve controls the flow of reactive gas from the tank into the distribution line such that the measured voltage agrees with a set voltage.
Lastly, an apparatus for the reactive coating of a substrate is described in an older, not previously published patent application (German P 41 36 655.7; addition to P 40 42 289.5), in which a cathode which is separated electrically from the vacuum chamber, is configured as a magnetron cathode and comprises two parts electrically separated from one another, in which the target base body with yoke and magnet is coupled as the one part, with the interposition of a capacitor, to the negative pole of a DC power supply, and the target as the other part is connected to the power supply by a conductor, with the interposition of a choke and a resistor parallel to the latter. The target is coupled by an additional capacitor to the positive pole of the power supply and to the anode, which in turn is grounded, with the interposition of a resistor. An inductor is inserted into the branch line to the resistor and to the choke in series with the low-inductance capacitor, and the value of the resistor is typically between 2 thousand and 10 thousand ohms.
This older apparatus is already so constructed that it suppresses most of the arcs occurring during a coating process and reduces the energy of the arcs and improves the reignition of the plasma after an arc.